1. Field of the Invention
The present invention relates to a rotary electric machine capable of suppressing a cogging torque without reducing torque and also relates to an electric wheelchair (or electrically powered wheelchair) mounted with such rotary electric machine.
2. Related Art
In a known art, as such a rotary electric machine, there has been provided an axial gap type rotary electric machine as shown, for example, in FIG. 21, in which the rotary electric machine has a stator 3 provided with teeth 2 and a rotor provided with a plurality of magnets (permanent magnets) which are disposed with a gap in a rotation axis direction.
More in detail, the each tooth (each of the teeth) 2 is composed of a plurality of steel plate sheets 2a laminated in a radial direction thereof, and a plurality of such teeth 2 are arranged and fixed side by side in the circumferential direction of a disc, i.e., substantially ring-shaped, stator yoke core. Coils are wound up around these teeth 2 through insulating material such as bobbins, not shown. Further, the teeth 2, the stator yoke and the coils are integrally fixed by means of molding resin 7 such that surfaces 2b of the teeth 2 opposing to the rotor are exposed outward.
The tooth 2 is formed by laminating a plurality of steel plates 2a having the same shapes for reducing processing cost including mold cost, and a slot (gap) S is formed between the adjacent teeth 2 for a coiling space, for example. When the rotor 3 is rotated, a torque is changed between a portion corresponding to the slot S and a portion corresponding to an opposing surface 2b of the tooth 2, thus causing a large cogging torque, which may result in generation of vibration or noise.
There are provided conventional technologies for reducing the cogging torque, such as disclosed in Japanese Patent Laid-open Application Publication No. HEI 11-18326 (Reference 1), in which dummy slot is formed at a central portion of the tooth, in the Japanese Patent Laid-open Application Publication No. 2004-80944 (P2004-80944A) (reference 2), in which a skew is formed to a stator core plate, and in the Japanese Patent Laid-open Application Publication No. HEI 10-126982 (Reference 3), in which the teeth are arranged with unequal pitches.
In the technologies mentioned above, however, in the case where the adjacent magnets and/or adjacent teeth include a wide distance therebetween, it was difficult to sufficiently reduce the cogging torque. Moreover, in the technologies of the References 2 and 3, the lamination process of the steel plates and the winding process of the coil involved complicated and troublesome workings, resulting in an increase in cost.
Moreover, in order to reduce the cogging torque, if the level of the skew disclosed in the Reference 2 and the unequal pitch disclosed in the Reference 3 are increased, resulting in decrease in an output torque, thus being inconvenient.
Especially, in the axial gap type rotary electric machine, the widths L1 and L2 of the slot openings on the inner and outer diameter sides of the adjacent teeth 2 may differ, and moreover, on the outer diameter side, the width L2 may further be larger than the gap (slot) in a general rotary electric machine (i.e., radial gap type or like). In such conventional cogging torque reducing technologies, it was accordingly difficult to reduce the cogging torque without reducing or deteriorating driving performance of the machine.